Expand Session watcher to help auto complete with NSE (tidyverse syntax)

It would be awesome if the session watchers autocomplete could be expanded to work with non-standard evaluation for example when using dplyr’s mutate/select/etc.

I.e. when writing something like:

iris %>%
    select( 

Then have the auto-complete popup with the list of variables within the iris dataset.

[renkun-ken]

I filed https://github.com/REditorSupport/languageserver/pull/369 that adds ( to the completion trigger characters in languageserver.

[renkun-ken]

To provide completion items in a pipe expression, without a parser, it is a bit trickier to detect the names of the variables to show completions, although we already have the names() of all variables in the global environment in globalenv.json created by the session watcher. I suggest we do the following:

my_dt %>%
  mutate(var3 = test) %>%
  select(var1, var2, var3)

As a starting point, we should detect my_dt in this case, and hopefully var3 in the future.